The present invention relates to an electric power steering apparatus that assists steering operation by a driver.
Electric power steering apparatuses have been known that assist a driver's steering operation by applying assist torque from a motor to a vehicle steering mechanism. Japanese Patent No. 4453012 describes an example of such an electric power steering apparatus.
The electric power steering apparatus of Japanese Patent No. 4453012 has a first reference model and a second reference model. The first reference model defines a target steering torque based on a steered angle of a steering wheel. The second reference model defines a target steered angle of steerable wheels based on a steering torque of the steering wheel. Driving of the motor is controlled based on these two reference models (ideal models). Specifically, this electric power steering apparatus determines a first assist component by executing torque feedback control to cause the actual steering torque to agree with a target steering torque and determines a second assist component by executing steered angle feedback control to cause the actual steered angle to agree with a target steered angle. Driving of the motor is controlled based on a value obtained by adding the first and second assist components. This configuration applies an assist torque determined based on the first assist component, so that a steering torque can always be set at an optimum value. Further, this configuration applies an assist torque determined based on the second assist component, so that reverse input vibration transferred from the steerable wheels can be canceled.